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TOMOYO Linux Cross Reference
Linux/kernel/exit.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  *  linux/kernel/exit.c
  4  *
  5  *  Copyright (C) 1991, 1992  Linus Torvalds
  6  */
  7 
  8 #include <linux/mm.h>
  9 #include <linux/slab.h>
 10 #include <linux/sched/autogroup.h>
 11 #include <linux/sched/mm.h>
 12 #include <linux/sched/stat.h>
 13 #include <linux/sched/task.h>
 14 #include <linux/sched/task_stack.h>
 15 #include <linux/sched/cputime.h>
 16 #include <linux/interrupt.h>
 17 #include <linux/module.h>
 18 #include <linux/capability.h>
 19 #include <linux/completion.h>
 20 #include <linux/personality.h>
 21 #include <linux/tty.h>
 22 #include <linux/iocontext.h>
 23 #include <linux/key.h>
 24 #include <linux/cpu.h>
 25 #include <linux/acct.h>
 26 #include <linux/tsacct_kern.h>
 27 #include <linux/file.h>
 28 #include <linux/fdtable.h>
 29 #include <linux/freezer.h>
 30 #include <linux/binfmts.h>
 31 #include <linux/nsproxy.h>
 32 #include <linux/pid_namespace.h>
 33 #include <linux/ptrace.h>
 34 #include <linux/profile.h>
 35 #include <linux/mount.h>
 36 #include <linux/proc_fs.h>
 37 #include <linux/kthread.h>
 38 #include <linux/mempolicy.h>
 39 #include <linux/taskstats_kern.h>
 40 #include <linux/delayacct.h>
 41 #include <linux/cgroup.h>
 42 #include <linux/syscalls.h>
 43 #include <linux/signal.h>
 44 #include <linux/posix-timers.h>
 45 #include <linux/cn_proc.h>
 46 #include <linux/mutex.h>
 47 #include <linux/futex.h>
 48 #include <linux/pipe_fs_i.h>
 49 #include <linux/audit.h> /* for audit_free() */
 50 #include <linux/resource.h>
 51 #include <linux/task_io_accounting_ops.h>
 52 #include <linux/tracehook.h>
 53 #include <linux/fs_struct.h>
 54 #include <linux/init_task.h>
 55 #include <linux/perf_event.h>
 56 #include <trace/events/sched.h>
 57 #include <linux/hw_breakpoint.h>
 58 #include <linux/oom.h>
 59 #include <linux/writeback.h>
 60 #include <linux/shm.h>
 61 #include <linux/kcov.h>
 62 #include <linux/random.h>
 63 #include <linux/rcuwait.h>
 64 #include <linux/compat.h>
 65 #include <linux/io_uring.h>
 66 #include <linux/kprobes.h>
 67 
 68 #include <linux/uaccess.h>
 69 #include <asm/unistd.h>
 70 #include <asm/mmu_context.h>
 71 
 72 static void __unhash_process(struct task_struct *p, bool group_dead)
 73 {
 74         nr_threads--;
 75         detach_pid(p, PIDTYPE_PID);
 76         if (group_dead) {
 77                 detach_pid(p, PIDTYPE_TGID);
 78                 detach_pid(p, PIDTYPE_PGID);
 79                 detach_pid(p, PIDTYPE_SID);
 80 
 81                 list_del_rcu(&p->tasks);
 82                 list_del_init(&p->sibling);
 83                 __this_cpu_dec(process_counts);
 84         }
 85         list_del_rcu(&p->thread_group);
 86         list_del_rcu(&p->thread_node);
 87 }
 88 
 89 /*
 90  * This function expects the tasklist_lock write-locked.
 91  */
 92 static void __exit_signal(struct task_struct *tsk)
 93 {
 94         struct signal_struct *sig = tsk->signal;
 95         bool group_dead = thread_group_leader(tsk);
 96         struct sighand_struct *sighand;
 97         struct tty_struct *tty;
 98         u64 utime, stime;
 99 
100         sighand = rcu_dereference_check(tsk->sighand,
101                                         lockdep_tasklist_lock_is_held());
102         spin_lock(&sighand->siglock);
103 
104 #ifdef CONFIG_POSIX_TIMERS
105         posix_cpu_timers_exit(tsk);
106         if (group_dead)
107                 posix_cpu_timers_exit_group(tsk);
108 #endif
109 
110         if (group_dead) {
111                 tty = sig->tty;
112                 sig->tty = NULL;
113         } else {
114                 /*
115                  * If there is any task waiting for the group exit
116                  * then notify it:
117                  */
118                 if (sig->notify_count > 0 && !--sig->notify_count)
119                         wake_up_process(sig->group_exit_task);
120 
121                 if (tsk == sig->curr_target)
122                         sig->curr_target = next_thread(tsk);
123         }
124 
125         add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
126                               sizeof(unsigned long long));
127 
128         /*
129          * Accumulate here the counters for all threads as they die. We could
130          * skip the group leader because it is the last user of signal_struct,
131          * but we want to avoid the race with thread_group_cputime() which can
132          * see the empty ->thread_head list.
133          */
134         task_cputime(tsk, &utime, &stime);
135         write_seqlock(&sig->stats_lock);
136         sig->utime += utime;
137         sig->stime += stime;
138         sig->gtime += task_gtime(tsk);
139         sig->min_flt += tsk->min_flt;
140         sig->maj_flt += tsk->maj_flt;
141         sig->nvcsw += tsk->nvcsw;
142         sig->nivcsw += tsk->nivcsw;
143         sig->inblock += task_io_get_inblock(tsk);
144         sig->oublock += task_io_get_oublock(tsk);
145         task_io_accounting_add(&sig->ioac, &tsk->ioac);
146         sig->sum_sched_runtime += tsk->se.sum_exec_runtime;
147         sig->nr_threads--;
148         __unhash_process(tsk, group_dead);
149         write_sequnlock(&sig->stats_lock);
150 
151         /*
152          * Do this under ->siglock, we can race with another thread
153          * doing sigqueue_free() if we have SIGQUEUE_PREALLOC signals.
154          */
155         flush_sigqueue(&tsk->pending);
156         tsk->sighand = NULL;
157         spin_unlock(&sighand->siglock);
158 
159         __cleanup_sighand(sighand);
160         clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
161         if (group_dead) {
162                 flush_sigqueue(&sig->shared_pending);
163                 tty_kref_put(tty);
164         }
165 }
166 
167 static void delayed_put_task_struct(struct rcu_head *rhp)
168 {
169         struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
170 
171         kprobe_flush_task(tsk);
172         perf_event_delayed_put(tsk);
173         trace_sched_process_free(tsk);
174         put_task_struct(tsk);
175 }
176 
177 void put_task_struct_rcu_user(struct task_struct *task)
178 {
179         if (refcount_dec_and_test(&task->rcu_users))
180                 call_rcu(&task->rcu, delayed_put_task_struct);
181 }
182 
183 void release_task(struct task_struct *p)
184 {
185         struct task_struct *leader;
186         struct pid *thread_pid;
187         int zap_leader;
188 repeat:
189         /* don't need to get the RCU readlock here - the process is dead and
190          * can't be modifying its own credentials. But shut RCU-lockdep up */
191         rcu_read_lock();
192         dec_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
193         rcu_read_unlock();
194 
195         cgroup_release(p);
196 
197         write_lock_irq(&tasklist_lock);
198         ptrace_release_task(p);
199         thread_pid = get_pid(p->thread_pid);
200         __exit_signal(p);
201 
202         /*
203          * If we are the last non-leader member of the thread
204          * group, and the leader is zombie, then notify the
205          * group leader's parent process. (if it wants notification.)
206          */
207         zap_leader = 0;
208         leader = p->group_leader;
209         if (leader != p && thread_group_empty(leader)
210                         && leader->exit_state == EXIT_ZOMBIE) {
211                 /*
212                  * If we were the last child thread and the leader has
213                  * exited already, and the leader's parent ignores SIGCHLD,
214                  * then we are the one who should release the leader.
215                  */
216                 zap_leader = do_notify_parent(leader, leader->exit_signal);
217                 if (zap_leader)
218                         leader->exit_state = EXIT_DEAD;
219         }
220 
221         write_unlock_irq(&tasklist_lock);
222         seccomp_filter_release(p);
223         proc_flush_pid(thread_pid);
224         put_pid(thread_pid);
225         release_thread(p);
226         put_task_struct_rcu_user(p);
227 
228         p = leader;
229         if (unlikely(zap_leader))
230                 goto repeat;
231 }
232 
233 int rcuwait_wake_up(struct rcuwait *w)
234 {
235         int ret = 0;
236         struct task_struct *task;
237 
238         rcu_read_lock();
239 
240         /*
241          * Order condition vs @task, such that everything prior to the load
242          * of @task is visible. This is the condition as to why the user called
243          * rcuwait_wake() in the first place. Pairs with set_current_state()
244          * barrier (A) in rcuwait_wait_event().
245          *
246          *    WAIT                WAKE
247          *    [S] tsk = current   [S] cond = true
248          *        MB (A)              MB (B)
249          *    [L] cond            [L] tsk
250          */
251         smp_mb(); /* (B) */
252 
253         task = rcu_dereference(w->task);
254         if (task)
255                 ret = wake_up_process(task);
256         rcu_read_unlock();
257 
258         return ret;
259 }
260 EXPORT_SYMBOL_GPL(rcuwait_wake_up);
261 
262 /*
263  * Determine if a process group is "orphaned", according to the POSIX
264  * definition in 2.2.2.52.  Orphaned process groups are not to be affected
265  * by terminal-generated stop signals.  Newly orphaned process groups are
266  * to receive a SIGHUP and a SIGCONT.
267  *
268  * "I ask you, have you ever known what it is to be an orphan?"
269  */
270 static int will_become_orphaned_pgrp(struct pid *pgrp,
271                                         struct task_struct *ignored_task)
272 {
273         struct task_struct *p;
274 
275         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
276                 if ((p == ignored_task) ||
277                     (p->exit_state && thread_group_empty(p)) ||
278                     is_global_init(p->real_parent))
279                         continue;
280 
281                 if (task_pgrp(p->real_parent) != pgrp &&
282                     task_session(p->real_parent) == task_session(p))
283                         return 0;
284         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
285 
286         return 1;
287 }
288 
289 int is_current_pgrp_orphaned(void)
290 {
291         int retval;
292 
293         read_lock(&tasklist_lock);
294         retval = will_become_orphaned_pgrp(task_pgrp(current), NULL);
295         read_unlock(&tasklist_lock);
296 
297         return retval;
298 }
299 
300 static bool has_stopped_jobs(struct pid *pgrp)
301 {
302         struct task_struct *p;
303 
304         do_each_pid_task(pgrp, PIDTYPE_PGID, p) {
305                 if (p->signal->flags & SIGNAL_STOP_STOPPED)
306                         return true;
307         } while_each_pid_task(pgrp, PIDTYPE_PGID, p);
308 
309         return false;
310 }
311 
312 /*
313  * Check to see if any process groups have become orphaned as
314  * a result of our exiting, and if they have any stopped jobs,
315  * send them a SIGHUP and then a SIGCONT. (POSIX 3.2.2.2)
316  */
317 static void
318 kill_orphaned_pgrp(struct task_struct *tsk, struct task_struct *parent)
319 {
320         struct pid *pgrp = task_pgrp(tsk);
321         struct task_struct *ignored_task = tsk;
322 
323         if (!parent)
324                 /* exit: our father is in a different pgrp than
325                  * we are and we were the only connection outside.
326                  */
327                 parent = tsk->real_parent;
328         else
329                 /* reparent: our child is in a different pgrp than
330                  * we are, and it was the only connection outside.
331                  */
332                 ignored_task = NULL;
333 
334         if (task_pgrp(parent) != pgrp &&
335             task_session(parent) == task_session(tsk) &&
336             will_become_orphaned_pgrp(pgrp, ignored_task) &&
337             has_stopped_jobs(pgrp)) {
338                 __kill_pgrp_info(SIGHUP, SEND_SIG_PRIV, pgrp);
339                 __kill_pgrp_info(SIGCONT, SEND_SIG_PRIV, pgrp);
340         }
341 }
342 
343 static void coredump_task_exit(struct task_struct *tsk)
344 {
345         struct core_state *core_state;
346 
347         /*
348          * Serialize with any possible pending coredump.
349          * We must hold siglock around checking core_state
350          * and setting PF_POSTCOREDUMP.  The core-inducing thread
351          * will increment ->nr_threads for each thread in the
352          * group without PF_POSTCOREDUMP set.
353          */
354         spin_lock_irq(&tsk->sighand->siglock);
355         tsk->flags |= PF_POSTCOREDUMP;
356         core_state = tsk->signal->core_state;
357         spin_unlock_irq(&tsk->sighand->siglock);
358         if (core_state) {
359                 struct core_thread self;
360 
361                 self.task = current;
362                 if (self.task->flags & PF_SIGNALED)
363                         self.next = xchg(&core_state->dumper.next, &self);
364                 else
365                         self.task = NULL;
366                 /*
367                  * Implies mb(), the result of xchg() must be visible
368                  * to core_state->dumper.
369                  */
370                 if (atomic_dec_and_test(&core_state->nr_threads))
371                         complete(&core_state->startup);
372 
373                 for (;;) {
374                         set_current_state(TASK_UNINTERRUPTIBLE);
375                         if (!self.task) /* see coredump_finish() */
376                                 break;
377                         freezable_schedule();
378                 }
379                 __set_current_state(TASK_RUNNING);
380         }
381 }
382 
383 #ifdef CONFIG_MEMCG
384 /*
385  * A task is exiting.   If it owned this mm, find a new owner for the mm.
386  */
387 void mm_update_next_owner(struct mm_struct *mm)
388 {
389         struct task_struct *c, *g, *p = current;
390 
391 retry:
392         /*
393          * If the exiting or execing task is not the owner, it's
394          * someone else's problem.
395          */
396         if (mm->owner != p)
397                 return;
398         /*
399          * The current owner is exiting/execing and there are no other
400          * candidates.  Do not leave the mm pointing to a possibly
401          * freed task structure.
402          */
403         if (atomic_read(&mm->mm_users) <= 1) {
404                 WRITE_ONCE(mm->owner, NULL);
405                 return;
406         }
407 
408         read_lock(&tasklist_lock);
409         /*
410          * Search in the children
411          */
412         list_for_each_entry(c, &p->children, sibling) {
413                 if (c->mm == mm)
414                         goto assign_new_owner;
415         }
416 
417         /*
418          * Search in the siblings
419          */
420         list_for_each_entry(c, &p->real_parent->children, sibling) {
421                 if (c->mm == mm)
422                         goto assign_new_owner;
423         }
424 
425         /*
426          * Search through everything else, we should not get here often.
427          */
428         for_each_process(g) {
429                 if (g->flags & PF_KTHREAD)
430                         continue;
431                 for_each_thread(g, c) {
432                         if (c->mm == mm)
433                                 goto assign_new_owner;
434                         if (c->mm)
435                                 break;
436                 }
437         }
438         read_unlock(&tasklist_lock);
439         /*
440          * We found no owner yet mm_users > 1: this implies that we are
441          * most likely racing with swapoff (try_to_unuse()) or /proc or
442          * ptrace or page migration (get_task_mm()).  Mark owner as NULL.
443          */
444         WRITE_ONCE(mm->owner, NULL);
445         return;
446 
447 assign_new_owner:
448         BUG_ON(c == p);
449         get_task_struct(c);
450         /*
451          * The task_lock protects c->mm from changing.
452          * We always want mm->owner->mm == mm
453          */
454         task_lock(c);
455         /*
456          * Delay read_unlock() till we have the task_lock()
457          * to ensure that c does not slip away underneath us
458          */
459         read_unlock(&tasklist_lock);
460         if (c->mm != mm) {
461                 task_unlock(c);
462                 put_task_struct(c);
463                 goto retry;
464         }
465         WRITE_ONCE(mm->owner, c);
466         task_unlock(c);
467         put_task_struct(c);
468 }
469 #endif /* CONFIG_MEMCG */
470 
471 /*
472  * Turn us into a lazy TLB process if we
473  * aren't already..
474  */
475 static void exit_mm(void)
476 {
477         struct mm_struct *mm = current->mm;
478 
479         exit_mm_release(current, mm);
480         if (!mm)
481                 return;
482         sync_mm_rss(mm);
483         mmap_read_lock(mm);
484         mmgrab(mm);
485         BUG_ON(mm != current->active_mm);
486         /* more a memory barrier than a real lock */
487         task_lock(current);
488         /*
489          * When a thread stops operating on an address space, the loop
490          * in membarrier_private_expedited() may not observe that
491          * tsk->mm, and the loop in membarrier_global_expedited() may
492          * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED
493          * rq->membarrier_state, so those would not issue an IPI.
494          * Membarrier requires a memory barrier after accessing
495          * user-space memory, before clearing tsk->mm or the
496          * rq->membarrier_state.
497          */
498         smp_mb__after_spinlock();
499         local_irq_disable();
500         current->mm = NULL;
501         membarrier_update_current_mm(NULL);
502         enter_lazy_tlb(mm, current);
503         local_irq_enable();
504         task_unlock(current);
505         mmap_read_unlock(mm);
506         mm_update_next_owner(mm);
507         mmput(mm);
508         if (test_thread_flag(TIF_MEMDIE))
509                 exit_oom_victim();
510 }
511 
512 static struct task_struct *find_alive_thread(struct task_struct *p)
513 {
514         struct task_struct *t;
515 
516         for_each_thread(p, t) {
517                 if (!(t->flags & PF_EXITING))
518                         return t;
519         }
520         return NULL;
521 }
522 
523 static struct task_struct *find_child_reaper(struct task_struct *father,
524                                                 struct list_head *dead)
525         __releases(&tasklist_lock)
526         __acquires(&tasklist_lock)
527 {
528         struct pid_namespace *pid_ns = task_active_pid_ns(father);
529         struct task_struct *reaper = pid_ns->child_reaper;
530         struct task_struct *p, *n;
531 
532         if (likely(reaper != father))
533                 return reaper;
534 
535         reaper = find_alive_thread(father);
536         if (reaper) {
537                 pid_ns->child_reaper = reaper;
538                 return reaper;
539         }
540 
541         write_unlock_irq(&tasklist_lock);
542 
543         list_for_each_entry_safe(p, n, dead, ptrace_entry) {
544                 list_del_init(&p->ptrace_entry);
545                 release_task(p);
546         }
547 
548         zap_pid_ns_processes(pid_ns);
549         write_lock_irq(&tasklist_lock);
550 
551         return father;
552 }
553 
554 /*
555  * When we die, we re-parent all our children, and try to:
556  * 1. give them to another thread in our thread group, if such a member exists
557  * 2. give it to the first ancestor process which prctl'd itself as a
558  *    child_subreaper for its children (like a service manager)
559  * 3. give it to the init process (PID 1) in our pid namespace
560  */
561 static struct task_struct *find_new_reaper(struct task_struct *father,
562                                            struct task_struct *child_reaper)
563 {
564         struct task_struct *thread, *reaper;
565 
566         thread = find_alive_thread(father);
567         if (thread)
568                 return thread;
569 
570         if (father->signal->has_child_subreaper) {
571                 unsigned int ns_level = task_pid(father)->level;
572                 /*
573                  * Find the first ->is_child_subreaper ancestor in our pid_ns.
574                  * We can't check reaper != child_reaper to ensure we do not
575                  * cross the namespaces, the exiting parent could be injected
576                  * by setns() + fork().
577                  * We check pid->level, this is slightly more efficient than
578                  * task_active_pid_ns(reaper) != task_active_pid_ns(father).
579                  */
580                 for (reaper = father->real_parent;
581                      task_pid(reaper)->level == ns_level;
582                      reaper = reaper->real_parent) {
583                         if (reaper == &init_task)
584                                 break;
585                         if (!reaper->signal->is_child_subreaper)
586                                 continue;
587                         thread = find_alive_thread(reaper);
588                         if (thread)
589                                 return thread;
590                 }
591         }
592 
593         return child_reaper;
594 }
595 
596 /*
597 * Any that need to be release_task'd are put on the @dead list.
598  */
599 static void reparent_leader(struct task_struct *father, struct task_struct *p,
600                                 struct list_head *dead)
601 {
602         if (unlikely(p->exit_state == EXIT_DEAD))
603                 return;
604 
605         /* We don't want people slaying init. */
606         p->exit_signal = SIGCHLD;
607 
608         /* If it has exited notify the new parent about this child's death. */
609         if (!p->ptrace &&
610             p->exit_state == EXIT_ZOMBIE && thread_group_empty(p)) {
611                 if (do_notify_parent(p, p->exit_signal)) {
612                         p->exit_state = EXIT_DEAD;
613                         list_add(&p->ptrace_entry, dead);
614                 }
615         }
616 
617         kill_orphaned_pgrp(p, father);
618 }
619 
620 /*
621  * This does two things:
622  *
623  * A.  Make init inherit all the child processes
624  * B.  Check to see if any process groups have become orphaned
625  *      as a result of our exiting, and if they have any stopped
626  *      jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
627  */
628 static void forget_original_parent(struct task_struct *father,
629                                         struct list_head *dead)
630 {
631         struct task_struct *p, *t, *reaper;
632 
633         if (unlikely(!list_empty(&father->ptraced)))
634                 exit_ptrace(father, dead);
635 
636         /* Can drop and reacquire tasklist_lock */
637         reaper = find_child_reaper(father, dead);
638         if (list_empty(&father->children))
639                 return;
640 
641         reaper = find_new_reaper(father, reaper);
642         list_for_each_entry(p, &father->children, sibling) {
643                 for_each_thread(p, t) {
644                         RCU_INIT_POINTER(t->real_parent, reaper);
645                         BUG_ON((!t->ptrace) != (rcu_access_pointer(t->parent) == father));
646                         if (likely(!t->ptrace))
647                                 t->parent = t->real_parent;
648                         if (t->pdeath_signal)
649                                 group_send_sig_info(t->pdeath_signal,
650                                                     SEND_SIG_NOINFO, t,
651                                                     PIDTYPE_TGID);
652                 }
653                 /*
654                  * If this is a threaded reparent there is no need to
655                  * notify anyone anything has happened.
656                  */
657                 if (!same_thread_group(reaper, father))
658                         reparent_leader(father, p, dead);
659         }
660         list_splice_tail_init(&father->children, &reaper->children);
661 }
662 
663 /*
664  * Send signals to all our closest relatives so that they know
665  * to properly mourn us..
666  */
667 static void exit_notify(struct task_struct *tsk, int group_dead)
668 {
669         bool autoreap;
670         struct task_struct *p, *n;
671         LIST_HEAD(dead);
672 
673         write_lock_irq(&tasklist_lock);
674         forget_original_parent(tsk, &dead);
675 
676         if (group_dead)
677                 kill_orphaned_pgrp(tsk->group_leader, NULL);
678 
679         tsk->exit_state = EXIT_ZOMBIE;
680         if (unlikely(tsk->ptrace)) {
681                 int sig = thread_group_leader(tsk) &&
682                                 thread_group_empty(tsk) &&
683                                 !ptrace_reparented(tsk) ?
684                         tsk->exit_signal : SIGCHLD;
685                 autoreap = do_notify_parent(tsk, sig);
686         } else if (thread_group_leader(tsk)) {
687                 autoreap = thread_group_empty(tsk) &&
688                         do_notify_parent(tsk, tsk->exit_signal);
689         } else {
690                 autoreap = true;
691         }
692 
693         if (autoreap) {
694                 tsk->exit_state = EXIT_DEAD;
695                 list_add(&tsk->ptrace_entry, &dead);
696         }
697 
698         /* mt-exec, de_thread() is waiting for group leader */
699         if (unlikely(tsk->signal->notify_count < 0))
700                 wake_up_process(tsk->signal->group_exit_task);
701         write_unlock_irq(&tasklist_lock);
702 
703         list_for_each_entry_safe(p, n, &dead, ptrace_entry) {
704                 list_del_init(&p->ptrace_entry);
705                 release_task(p);
706         }
707 }
708 
709 #ifdef CONFIG_DEBUG_STACK_USAGE
710 static void check_stack_usage(void)
711 {
712         static DEFINE_SPINLOCK(low_water_lock);
713         static int lowest_to_date = THREAD_SIZE;
714         unsigned long free;
715 
716         free = stack_not_used(current);
717 
718         if (free >= lowest_to_date)
719                 return;
720 
721         spin_lock(&low_water_lock);
722         if (free < lowest_to_date) {
723                 pr_info("%s (%d) used greatest stack depth: %lu bytes left\n",
724                         current->comm, task_pid_nr(current), free);
725                 lowest_to_date = free;
726         }
727         spin_unlock(&low_water_lock);
728 }
729 #else
730 static inline void check_stack_usage(void) {}
731 #endif
732 
733 void __noreturn do_exit(long code)
734 {
735         struct task_struct *tsk = current;
736         int group_dead;
737 
738         /*
739          * We can get here from a kernel oops, sometimes with preemption off.
740          * Start by checking for critical errors.
741          * Then fix up important state like USER_DS and preemption.
742          * Then do everything else.
743          */
744 
745         WARN_ON(blk_needs_flush_plug(tsk));
746 
747         if (unlikely(in_interrupt()))
748                 panic("Aiee, killing interrupt handler!");
749         if (unlikely(!tsk->pid))
750                 panic("Attempted to kill the idle task!");
751 
752         /*
753          * If do_exit is called because this processes oopsed, it's possible
754          * that get_fs() was left as KERNEL_DS, so reset it to USER_DS before
755          * continuing. Amongst other possible reasons, this is to prevent
756          * mm_release()->clear_child_tid() from writing to a user-controlled
757          * kernel address.
758          */
759         force_uaccess_begin();
760 
761         if (unlikely(in_atomic())) {
762                 pr_info("note: %s[%d] exited with preempt_count %d\n",
763                         current->comm, task_pid_nr(current),
764                         preempt_count());
765                 preempt_count_set(PREEMPT_ENABLED);
766         }
767 
768         profile_task_exit(tsk);
769         kcov_task_exit(tsk);
770 
771         coredump_task_exit(tsk);
772         ptrace_event(PTRACE_EVENT_EXIT, code);
773 
774         validate_creds_for_do_exit(tsk);
775 
776         /*
777          * We're taking recursive faults here in do_exit. Safest is to just
778          * leave this task alone and wait for reboot.
779          */
780         if (unlikely(tsk->flags & PF_EXITING)) {
781                 pr_alert("Fixing recursive fault but reboot is needed!\n");
782                 futex_exit_recursive(tsk);
783                 set_current_state(TASK_UNINTERRUPTIBLE);
784                 schedule();
785         }
786 
787         io_uring_files_cancel();
788         exit_signals(tsk);  /* sets PF_EXITING */
789 
790         /* sync mm's RSS info before statistics gathering */
791         if (tsk->mm)
792                 sync_mm_rss(tsk->mm);
793         acct_update_integrals(tsk);
794         group_dead = atomic_dec_and_test(&tsk->signal->live);
795         if (group_dead) {
796                 /*
797                  * If the last thread of global init has exited, panic
798                  * immediately to get a useable coredump.
799                  */
800                 if (unlikely(is_global_init(tsk)))
801                         panic("Attempted to kill init! exitcode=0x%08x\n",
802                                 tsk->signal->group_exit_code ?: (int)code);
803 
804 #ifdef CONFIG_POSIX_TIMERS
805                 hrtimer_cancel(&tsk->signal->real_timer);
806                 exit_itimers(tsk->signal);
807 #endif
808                 if (tsk->mm)
809                         setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);
810         }
811         acct_collect(code, group_dead);
812         if (group_dead)
813                 tty_audit_exit();
814         audit_free(tsk);
815 
816         tsk->exit_code = code;
817         taskstats_exit(tsk, group_dead);
818 
819         exit_mm();
820 
821         if (group_dead)
822                 acct_process();
823         trace_sched_process_exit(tsk);
824 
825         exit_sem(tsk);
826         exit_shm(tsk);
827         exit_files(tsk);
828         exit_fs(tsk);
829         if (group_dead)
830                 disassociate_ctty(1);
831         exit_task_namespaces(tsk);
832         exit_task_work(tsk);
833         exit_thread(tsk);
834 
835         /*
836          * Flush inherited counters to the parent - before the parent
837          * gets woken up by child-exit notifications.
838          *
839          * because of cgroup mode, must be called before cgroup_exit()
840          */
841         perf_event_exit_task(tsk);
842 
843         sched_autogroup_exit_task(tsk);
844         cgroup_exit(tsk);
845 
846         /*
847          * FIXME: do that only when needed, using sched_exit tracepoint
848          */
849         flush_ptrace_hw_breakpoint(tsk);
850 
851         exit_tasks_rcu_start();
852         exit_notify(tsk, group_dead);
853         proc_exit_connector(tsk);
854         mpol_put_task_policy(tsk);
855 #ifdef CONFIG_FUTEX
856         if (unlikely(current->pi_state_cache))
857                 kfree(current->pi_state_cache);
858 #endif
859         /*
860          * Make sure we are holding no locks:
861          */
862         debug_check_no_locks_held();
863 
864         if (tsk->io_context)
865                 exit_io_context(tsk);
866 
867         if (tsk->splice_pipe)
868                 free_pipe_info(tsk->splice_pipe);
869 
870         if (tsk->task_frag.page)
871                 put_page(tsk->task_frag.page);
872 
873         validate_creds_for_do_exit(tsk);
874 
875         check_stack_usage();
876         preempt_disable();
877         if (tsk->nr_dirtied)
878                 __this_cpu_add(dirty_throttle_leaks, tsk->nr_dirtied);
879         exit_rcu();
880         exit_tasks_rcu_finish();
881 
882         lockdep_free_task(tsk);
883         do_task_dead();
884 }
885 EXPORT_SYMBOL_GPL(do_exit);
886 
887 void complete_and_exit(struct completion *comp, long code)
888 {
889         if (comp)
890                 complete(comp);
891 
892         do_exit(code);
893 }
894 EXPORT_SYMBOL(complete_and_exit);
895 
896 SYSCALL_DEFINE1(exit, int, error_code)
897 {
898         do_exit((error_code&0xff)<<8);
899 }
900 
901 /*
902  * Take down every thread in the group.  This is called by fatal signals
903  * as well as by sys_exit_group (below).
904  */
905 void
906 do_group_exit(int exit_code)
907 {
908         struct signal_struct *sig = current->signal;
909 
910         BUG_ON(exit_code & 0x80); /* core dumps don't get here */
911 
912         if (signal_group_exit(sig))
913                 exit_code = sig->group_exit_code;
914         else if (!thread_group_empty(current)) {
915                 struct sighand_struct *const sighand = current->sighand;
916 
917                 spin_lock_irq(&sighand->siglock);
918                 if (signal_group_exit(sig))
919                         /* Another thread got here before we took the lock.  */
920                         exit_code = sig->group_exit_code;
921                 else {
922                         sig->group_exit_code = exit_code;
923                         sig->flags = SIGNAL_GROUP_EXIT;
924                         zap_other_threads(current);
925                 }
926                 spin_unlock_irq(&sighand->siglock);
927         }
928 
929         do_exit(exit_code);
930         /* NOTREACHED */
931 }
932 
933 /*
934  * this kills every thread in the thread group. Note that any externally
935  * wait4()-ing process will get the correct exit code - even if this
936  * thread is not the thread group leader.
937  */
938 SYSCALL_DEFINE1(exit_group, int, error_code)
939 {
940         do_group_exit((error_code & 0xff) << 8);
941         /* NOTREACHED */
942         return 0;
943 }
944 
945 struct waitid_info {
946         pid_t pid;
947         uid_t uid;
948         int status;
949         int cause;
950 };
951 
952 struct wait_opts {
953         enum pid_type           wo_type;
954         int                     wo_flags;
955         struct pid              *wo_pid;
956 
957         struct waitid_info      *wo_info;
958         int                     wo_stat;
959         struct rusage           *wo_rusage;
960 
961         wait_queue_entry_t              child_wait;
962         int                     notask_error;
963 };
964 
965 static int eligible_pid(struct wait_opts *wo, struct task_struct *p)
966 {
967         return  wo->wo_type == PIDTYPE_MAX ||
968                 task_pid_type(p, wo->wo_type) == wo->wo_pid;
969 }
970 
971 static int
972 eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p)
973 {
974         if (!eligible_pid(wo, p))
975                 return 0;
976 
977         /*
978          * Wait for all children (clone and not) if __WALL is set or
979          * if it is traced by us.
980          */
981         if (ptrace || (wo->wo_flags & __WALL))
982                 return 1;
983 
984         /*
985          * Otherwise, wait for clone children *only* if __WCLONE is set;
986          * otherwise, wait for non-clone children *only*.
987          *
988          * Note: a "clone" child here is one that reports to its parent
989          * using a signal other than SIGCHLD, or a non-leader thread which
990          * we can only see if it is traced by us.
991          */
992         if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
993                 return 0;
994 
995         return 1;
996 }
997 
998 /*
999  * Handle sys_wait4 work for one task in state EXIT_ZOMBIE.  We hold
1000  * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
1001  * the lock and this task is uninteresting.  If we return nonzero, we have
1002  * released the lock and the system call should return.
1003  */
1004 static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
1005 {
1006         int state, status;
1007         pid_t pid = task_pid_vnr(p);
1008         uid_t uid = from_kuid_munged(current_user_ns(), task_uid(p));
1009         struct waitid_info *infop;
1010 
1011         if (!likely(wo->wo_flags & WEXITED))
1012                 return 0;
1013 
1014         if (unlikely(wo->wo_flags & WNOWAIT)) {
1015                 status = p->exit_code;
1016                 get_task_struct(p);
1017                 read_unlock(&tasklist_lock);
1018                 sched_annotate_sleep();
1019                 if (wo->wo_rusage)
1020                         getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1021                 put_task_struct(p);
1022                 goto out_info;
1023         }
1024         /*
1025          * Move the task's state to DEAD/TRACE, only one thread can do this.
1026          */
1027         state = (ptrace_reparented(p) && thread_group_leader(p)) ?
1028                 EXIT_TRACE : EXIT_DEAD;
1029         if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
1030                 return 0;
1031         /*
1032          * We own this thread, nobody else can reap it.
1033          */
1034         read_unlock(&tasklist_lock);
1035         sched_annotate_sleep();
1036 
1037         /*
1038          * Check thread_group_leader() to exclude the traced sub-threads.
1039          */
1040         if (state == EXIT_DEAD && thread_group_leader(p)) {
1041                 struct signal_struct *sig = p->signal;
1042                 struct signal_struct *psig = current->signal;
1043                 unsigned long maxrss;
1044                 u64 tgutime, tgstime;
1045 
1046                 /*
1047                  * The resource counters for the group leader are in its
1048                  * own task_struct.  Those for dead threads in the group
1049                  * are in its signal_struct, as are those for the child
1050                  * processes it has previously reaped.  All these
1051                  * accumulate in the parent's signal_struct c* fields.
1052                  *
1053                  * We don't bother to take a lock here to protect these
1054                  * p->signal fields because the whole thread group is dead
1055                  * and nobody can change them.
1056                  *
1057                  * psig->stats_lock also protects us from our sub-theads
1058                  * which can reap other children at the same time. Until
1059                  * we change k_getrusage()-like users to rely on this lock
1060                  * we have to take ->siglock as well.
1061                  *
1062                  * We use thread_group_cputime_adjusted() to get times for
1063                  * the thread group, which consolidates times for all threads
1064                  * in the group including the group leader.
1065                  */
1066                 thread_group_cputime_adjusted(p, &tgutime, &tgstime);
1067                 spin_lock_irq(&current->sighand->siglock);
1068                 write_seqlock(&psig->stats_lock);
1069                 psig->cutime += tgutime + sig->cutime;
1070                 psig->cstime += tgstime + sig->cstime;
1071                 psig->cgtime += task_gtime(p) + sig->gtime + sig->cgtime;
1072                 psig->cmin_flt +=
1073                         p->min_flt + sig->min_flt + sig->cmin_flt;
1074                 psig->cmaj_flt +=
1075                         p->maj_flt + sig->maj_flt + sig->cmaj_flt;
1076                 psig->cnvcsw +=
1077                         p->nvcsw + sig->nvcsw + sig->cnvcsw;
1078                 psig->cnivcsw +=
1079                         p->nivcsw + sig->nivcsw + sig->cnivcsw;
1080                 psig->cinblock +=
1081                         task_io_get_inblock(p) +
1082                         sig->inblock + sig->cinblock;
1083                 psig->coublock +=
1084                         task_io_get_oublock(p) +
1085                         sig->oublock + sig->coublock;
1086                 maxrss = max(sig->maxrss, sig->cmaxrss);
1087                 if (psig->cmaxrss < maxrss)
1088                         psig->cmaxrss = maxrss;
1089                 task_io_accounting_add(&psig->ioac, &p->ioac);
1090                 task_io_accounting_add(&psig->ioac, &sig->ioac);
1091                 write_sequnlock(&psig->stats_lock);
1092                 spin_unlock_irq(&current->sighand->siglock);
1093         }
1094 
1095         if (wo->wo_rusage)
1096                 getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1097         status = (p->signal->flags & SIGNAL_GROUP_EXIT)
1098                 ? p->signal->group_exit_code : p->exit_code;
1099         wo->wo_stat = status;
1100 
1101         if (state == EXIT_TRACE) {
1102                 write_lock_irq(&tasklist_lock);
1103                 /* We dropped tasklist, ptracer could die and untrace */
1104                 ptrace_unlink(p);
1105 
1106                 /* If parent wants a zombie, don't release it now */
1107                 state = EXIT_ZOMBIE;
1108                 if (do_notify_parent(p, p->exit_signal))
1109                         state = EXIT_DEAD;
1110                 p->exit_state = state;
1111                 write_unlock_irq(&tasklist_lock);
1112         }
1113         if (state == EXIT_DEAD)
1114                 release_task(p);
1115 
1116 out_info:
1117         infop = wo->wo_info;
1118         if (infop) {
1119                 if ((status & 0x7f) == 0) {
1120                         infop->cause = CLD_EXITED;
1121                         infop->status = status >> 8;
1122                 } else {
1123                         infop->cause = (status & 0x80) ? CLD_DUMPED : CLD_KILLED;
1124                         infop->status = status & 0x7f;
1125                 }
1126                 infop->pid = pid;
1127                 infop->uid = uid;
1128         }
1129 
1130         return pid;
1131 }
1132 
1133 static int *task_stopped_code(struct task_struct *p, bool ptrace)
1134 {
1135         if (ptrace) {
1136                 if (task_is_traced(p) && !(p->jobctl & JOBCTL_LISTENING))
1137                         return &p->exit_code;
1138         } else {
1139                 if (p->signal->flags & SIGNAL_STOP_STOPPED)
1140                         return &p->signal->group_exit_code;
1141         }
1142         return NULL;
1143 }
1144 
1145 /**
1146  * wait_task_stopped - Wait for %TASK_STOPPED or %TASK_TRACED
1147  * @wo: wait options
1148  * @ptrace: is the wait for ptrace
1149  * @p: task to wait for
1150  *
1151  * Handle sys_wait4() work for %p in state %TASK_STOPPED or %TASK_TRACED.
1152  *
1153  * CONTEXT:
1154  * read_lock(&tasklist_lock), which is released if return value is
1155  * non-zero.  Also, grabs and releases @p->sighand->siglock.
1156  *
1157  * RETURNS:
1158  * 0 if wait condition didn't exist and search for other wait conditions
1159  * should continue.  Non-zero return, -errno on failure and @p's pid on
1160  * success, implies that tasklist_lock is released and wait condition
1161  * search should terminate.
1162  */
1163 static int wait_task_stopped(struct wait_opts *wo,
1164                                 int ptrace, struct task_struct *p)
1165 {
1166         struct waitid_info *infop;
1167         int exit_code, *p_code, why;
1168         uid_t uid = 0; /* unneeded, required by compiler */
1169         pid_t pid;
1170 
1171         /*
1172          * Traditionally we see ptrace'd stopped tasks regardless of options.
1173          */
1174         if (!ptrace && !(wo->wo_flags & WUNTRACED))
1175                 return 0;
1176 
1177         if (!task_stopped_code(p, ptrace))
1178                 return 0;
1179 
1180         exit_code = 0;
1181         spin_lock_irq(&p->sighand->siglock);
1182 
1183         p_code = task_stopped_code(p, ptrace);
1184         if (unlikely(!p_code))
1185                 goto unlock_sig;
1186 
1187         exit_code = *p_code;
1188         if (!exit_code)
1189                 goto unlock_sig;
1190 
1191         if (!unlikely(wo->wo_flags & WNOWAIT))
1192                 *p_code = 0;
1193 
1194         uid = from_kuid_munged(current_user_ns(), task_uid(p));
1195 unlock_sig:
1196         spin_unlock_irq(&p->sighand->siglock);
1197         if (!exit_code)
1198                 return 0;
1199 
1200         /*
1201          * Now we are pretty sure this task is interesting.
1202          * Make sure it doesn't get reaped out from under us while we
1203          * give up the lock and then examine it below.  We don't want to
1204          * keep holding onto the tasklist_lock while we call getrusage and
1205          * possibly take page faults for user memory.
1206          */
1207         get_task_struct(p);
1208         pid = task_pid_vnr(p);
1209         why = ptrace ? CLD_TRAPPED : CLD_STOPPED;
1210         read_unlock(&tasklist_lock);
1211         sched_annotate_sleep();
1212         if (wo->wo_rusage)
1213                 getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1214         put_task_struct(p);
1215 
1216         if (likely(!(wo->wo_flags & WNOWAIT)))
1217                 wo->wo_stat = (exit_code << 8) | 0x7f;
1218 
1219         infop = wo->wo_info;
1220         if (infop) {
1221                 infop->cause = why;
1222                 infop->status = exit_code;
1223                 infop->pid = pid;
1224                 infop->uid = uid;
1225         }
1226         return pid;
1227 }
1228 
1229 /*
1230  * Handle do_wait work for one task in a live, non-stopped state.
1231  * read_lock(&tasklist_lock) on entry.  If we return zero, we still hold
1232  * the lock and this task is uninteresting.  If we return nonzero, we have
1233  * released the lock and the system call should return.
1234  */
1235 static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
1236 {
1237         struct waitid_info *infop;
1238         pid_t pid;
1239         uid_t uid;
1240 
1241         if (!unlikely(wo->wo_flags & WCONTINUED))
1242                 return 0;
1243 
1244         if (!(p->signal->flags & SIGNAL_STOP_CONTINUED))
1245                 return 0;
1246 
1247         spin_lock_irq(&p->sighand->siglock);
1248         /* Re-check with the lock held.  */
1249         if (!(p->signal->flags & SIGNAL_STOP_CONTINUED)) {
1250                 spin_unlock_irq(&p->sighand->siglock);
1251                 return 0;
1252         }
1253         if (!unlikely(wo->wo_flags & WNOWAIT))
1254                 p->signal->flags &= ~SIGNAL_STOP_CONTINUED;
1255         uid = from_kuid_munged(current_user_ns(), task_uid(p));
1256         spin_unlock_irq(&p->sighand->siglock);
1257 
1258         pid = task_pid_vnr(p);
1259         get_task_struct(p);
1260         read_unlock(&tasklist_lock);
1261         sched_annotate_sleep();
1262         if (wo->wo_rusage)
1263                 getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
1264         put_task_struct(p);
1265 
1266         infop = wo->wo_info;
1267         if (!infop) {
1268                 wo->wo_stat = 0xffff;
1269         } else {
1270                 infop->cause = CLD_CONTINUED;
1271                 infop->pid = pid;
1272                 infop->uid = uid;
1273                 infop->status = SIGCONT;
1274         }
1275         return pid;
1276 }
1277 
1278 /*
1279  * Consider @p for a wait by @parent.
1280  *
1281  * -ECHILD should be in ->notask_error before the first call.
1282  * Returns nonzero for a final return, when we have unlocked tasklist_lock.
1283  * Returns zero if the search for a child should continue;
1284  * then ->notask_error is 0 if @p is an eligible child,
1285  * or still -ECHILD.
1286  */
1287 static int wait_consider_task(struct wait_opts *wo, int ptrace,
1288                                 struct task_struct *p)
1289 {
1290         /*
1291          * We can race with wait_task_zombie() from another thread.
1292          * Ensure that EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE transition
1293          * can't confuse the checks below.
1294          */
1295         int exit_state = READ_ONCE(p->exit_state);
1296         int ret;
1297 
1298         if (unlikely(exit_state == EXIT_DEAD))
1299                 return 0;
1300 
1301         ret = eligible_child(wo, ptrace, p);
1302         if (!ret)
1303                 return ret;
1304 
1305         if (unlikely(exit_state == EXIT_TRACE)) {
1306                 /*
1307                  * ptrace == 0 means we are the natural parent. In this case
1308                  * we should clear notask_error, debugger will notify us.
1309                  */
1310                 if (likely(!ptrace))
1311                         wo->notask_error = 0;
1312                 return 0;
1313         }
1314 
1315         if (likely(!ptrace) && unlikely(p->ptrace)) {
1316                 /*
1317                  * If it is traced by its real parent's group, just pretend
1318                  * the caller is ptrace_do_wait() and reap this child if it
1319                  * is zombie.
1320                  *
1321                  * This also hides group stop state from real parent; otherwise
1322                  * a single stop can be reported twice as group and ptrace stop.
1323                  * If a ptracer wants to distinguish these two events for its
1324                  * own children it should create a separate process which takes
1325                  * the role of real parent.
1326                  */
1327                 if (!ptrace_reparented(p))
1328                         ptrace = 1;
1329         }
1330 
1331         /* slay zombie? */
1332         if (exit_state == EXIT_ZOMBIE) {
1333                 /* we don't reap group leaders with subthreads */
1334                 if (!delay_group_leader(p)) {
1335                         /*
1336                          * A zombie ptracee is only visible to its ptracer.
1337                          * Notification and reaping will be cascaded to the
1338                          * real parent when the ptracer detaches.
1339                          */
1340                         if (unlikely(ptrace) || likely(!p->ptrace))
1341                                 return wait_task_zombie(wo, p);
1342                 }
1343 
1344                 /*
1345                  * Allow access to stopped/continued state via zombie by
1346                  * falling through.  Clearing of notask_error is complex.
1347                  *
1348                  * When !@ptrace:
1349                  *
1350                  * If WEXITED is set, notask_error should naturally be
1351                  * cleared.  If not, subset of WSTOPPED|WCONTINUED is set,
1352                  * so, if there are live subthreads, there are events to
1353                  * wait for.  If all subthreads are dead, it's still safe
1354                  * to clear - this function will be called again in finite
1355                  * amount time once all the subthreads are released and
1356                  * will then return without clearing.
1357                  *
1358                  * When @ptrace:
1359                  *
1360                  * Stopped state is per-task and thus can't change once the
1361                  * target task dies.  Only continued and exited can happen.
1362                  * Clear notask_error if WCONTINUED | WEXITED.
1363                  */
1364                 if (likely(!ptrace) || (wo->wo_flags & (WCONTINUED | WEXITED)))
1365                         wo->notask_error = 0;
1366         } else {
1367                 /*
1368                  * @p is alive and it's gonna stop, continue or exit, so
1369                  * there always is something to wait for.
1370                  */
1371                 wo->notask_error = 0;
1372         }
1373 
1374         /*
1375          * Wait for stopped.  Depending on @ptrace, different stopped state
1376          * is used and the two don't interact with each other.
1377          */
1378         ret = wait_task_stopped(wo, ptrace, p);
1379         if (ret)
1380                 return ret;
1381 
1382         /*
1383          * Wait for continued.  There's only one continued state and the
1384          * ptracer can consume it which can confuse the real parent.  Don't
1385          * use WCONTINUED from ptracer.  You don't need or want it.
1386          */
1387         return wait_task_continued(wo, p);
1388 }
1389 
1390 /*
1391  * Do the work of do_wait() for one thread in the group, @tsk.
1392  *
1393  * -ECHILD should be in ->notask_error before the first call.
1394  * Returns nonzero for a final return, when we have unlocked tasklist_lock.
1395  * Returns zero if the search for a child should continue; then
1396  * ->notask_error is 0 if there were any eligible children,
1397  * or still -ECHILD.
1398  */
1399 static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
1400 {
1401         struct task_struct *p;
1402 
1403         list_for_each_entry(p, &tsk->children, sibling) {
1404                 int ret = wait_consider_task(wo, 0, p);
1405 
1406                 if (ret)
1407                         return ret;
1408         }
1409 
1410         return 0;
1411 }
1412 
1413 static int ptrace_do_wait(struct wait_opts *wo, struct task_struct *tsk)
1414 {
1415         struct task_struct *p;
1416 
1417         list_for_each_entry(p, &tsk->ptraced, ptrace_entry) {
1418                 int ret = wait_consider_task(wo, 1, p);
1419 
1420                 if (ret)
1421                         return ret;
1422         }
1423 
1424         return 0;
1425 }
1426 
1427 static int child_wait_callback(wait_queue_entry_t *wait, unsigned mode,
1428                                 int sync, void *key)
1429 {
1430         struct wait_opts *wo = container_of(wait, struct wait_opts,
1431                                                 child_wait);
1432         struct task_struct *p = key;
1433 
1434         if (!eligible_pid(wo, p))
1435                 return 0;
1436 
1437         if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
1438                 return 0;
1439 
1440         return default_wake_function(wait, mode, sync, key);
1441 }
1442 
1443 void __wake_up_parent(struct task_struct *p, struct task_struct *parent)
1444 {
1445         __wake_up_sync_key(&parent->signal->wait_chldexit,
1446                            TASK_INTERRUPTIBLE, p);
1447 }
1448 
1449 static bool is_effectively_child(struct wait_opts *wo, bool ptrace,
1450                                  struct task_struct *target)
1451 {
1452         struct task_struct *parent =
1453                 !ptrace ? target->real_parent : target->parent;
1454 
1455         return current == parent || (!(wo->wo_flags & __WNOTHREAD) &&
1456                                      same_thread_group(current, parent));
1457 }
1458 
1459 /*
1460  * Optimization for waiting on PIDTYPE_PID. No need to iterate through child
1461  * and tracee lists to find the target task.
1462  */
1463 static int do_wait_pid(struct wait_opts *wo)
1464 {
1465         bool ptrace;
1466         struct task_struct *target;
1467         int retval;
1468 
1469         ptrace = false;
1470         target = pid_task(wo->wo_pid, PIDTYPE_TGID);
1471         if (target && is_effectively_child(wo, ptrace, target)) {
1472                 retval = wait_consider_task(wo, ptrace, target);
1473                 if (retval)
1474                         return retval;
1475         }
1476 
1477         ptrace = true;
1478         target = pid_task(wo->wo_pid, PIDTYPE_PID);
1479         if (target && target->ptrace &&
1480             is_effectively_child(wo, ptrace, target)) {
1481                 retval = wait_consider_task(wo, ptrace, target);
1482                 if (retval)
1483                         return retval;
1484         }
1485 
1486         return 0;
1487 }
1488 
1489 static long do_wait(struct wait_opts *wo)
1490 {
1491         int retval;
1492 
1493         trace_sched_process_wait(wo->wo_pid);
1494 
1495         init_waitqueue_func_entry(&wo->child_wait, child_wait_callback);
1496         wo->child_wait.private = current;
1497         add_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
1498 repeat:
1499         /*
1500          * If there is nothing that can match our criteria, just get out.
1501          * We will clear ->notask_error to zero if we see any child that
1502          * might later match our criteria, even if we are not able to reap
1503          * it yet.
1504          */
1505         wo->notask_error = -ECHILD;
1506         if ((wo->wo_type < PIDTYPE_MAX) &&
1507            (!wo->wo_pid || !pid_has_task(wo->wo_pid, wo->wo_type)))
1508                 goto notask;
1509 
1510         set_current_state(TASK_INTERRUPTIBLE);
1511         read_lock(&tasklist_lock);
1512 
1513         if (wo->wo_type == PIDTYPE_PID) {
1514                 retval = do_wait_pid(wo);
1515                 if (retval)
1516                         goto end;
1517         } else {
1518                 struct task_struct *tsk = current;
1519 
1520                 do {
1521                         retval = do_wait_thread(wo, tsk);
1522                         if (retval)
1523                                 goto end;
1524 
1525                         retval = ptrace_do_wait(wo, tsk);
1526                         if (retval)
1527                                 goto end;
1528 
1529                         if (wo->wo_flags & __WNOTHREAD)
1530                                 break;
1531                 } while_each_thread(current, tsk);
1532         }
1533         read_unlock(&tasklist_lock);
1534 
1535 notask:
1536         retval = wo->notask_error;
1537         if (!retval && !(wo->wo_flags & WNOHANG)) {
1538                 retval = -ERESTARTSYS;
1539                 if (!signal_pending(current)) {
1540                         schedule();
1541                         goto repeat;
1542                 }
1543         }
1544 end:
1545         __set_current_state(TASK_RUNNING);
1546         remove_wait_queue(&current->signal->wait_chldexit, &wo->child_wait);
1547         return retval;
1548 }
1549 
1550 static long kernel_waitid(int which, pid_t upid, struct waitid_info *infop,
1551                           int options, struct rusage *ru)
1552 {
1553         struct wait_opts wo;
1554         struct pid *pid = NULL;
1555         enum pid_type type;
1556         long ret;
1557         unsigned int f_flags = 0;
1558 
1559         if (options & ~(WNOHANG|WNOWAIT|WEXITED|WSTOPPED|WCONTINUED|
1560                         __WNOTHREAD|__WCLONE|__WALL))
1561                 return -EINVAL;
1562         if (!(options & (WEXITED|WSTOPPED|WCONTINUED)))
1563                 return -EINVAL;
1564 
1565         switch (which) {
1566         case P_ALL:
1567                 type = PIDTYPE_MAX;
1568                 break;
1569         case P_PID:
1570                 type = PIDTYPE_PID;
1571                 if (upid <= 0)
1572                         return -EINVAL;
1573 
1574                 pid = find_get_pid(upid);
1575                 break;
1576         case P_PGID:
1577                 type = PIDTYPE_PGID;
1578                 if (upid < 0)
1579                         return -EINVAL;
1580 
1581                 if (upid)
1582                         pid = find_get_pid(upid);
1583                 else
1584                         pid = get_task_pid(current, PIDTYPE_PGID);
1585                 break;
1586         case P_PIDFD:
1587                 type = PIDTYPE_PID;
1588                 if (upid < 0)
1589                         return -EINVAL;
1590 
1591                 pid = pidfd_get_pid(upid, &f_flags);
1592                 if (IS_ERR(pid))
1593                         return PTR_ERR(pid);
1594 
1595                 break;
1596         default:
1597                 return -EINVAL;
1598         }
1599 
1600         wo.wo_type      = type;
1601         wo.wo_pid       = pid;
1602         wo.wo_flags     = options;
1603         wo.wo_info      = infop;
1604         wo.wo_rusage    = ru;
1605         if (f_flags & O_NONBLOCK)
1606                 wo.wo_flags |= WNOHANG;
1607 
1608         ret = do_wait(&wo);
1609         if (!ret && !(options & WNOHANG) && (f_flags & O_NONBLOCK))
1610                 ret = -EAGAIN;
1611 
1612         put_pid(pid);
1613         return ret;
1614 }
1615 
1616 SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
1617                 infop, int, options, struct rusage __user *, ru)
1618 {
1619         struct rusage r;
1620         struct waitid_info info = {.status = 0};
1621         long err = kernel_waitid(which, upid, &info, options, ru ? &r : NULL);
1622         int signo = 0;
1623 
1624         if (err > 0) {
1625                 signo = SIGCHLD;
1626                 err = 0;
1627                 if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
1628                         return -EFAULT;
1629         }
1630         if (!infop)
1631                 return err;
1632 
1633         if (!user_write_access_begin(infop, sizeof(*infop)))
1634                 return -EFAULT;
1635 
1636         unsafe_put_user(signo, &infop->si_signo, Efault);
1637         unsafe_put_user(0, &infop->si_errno, Efault);
1638         unsafe_put_user(info.cause, &infop->si_code, Efault);
1639         unsafe_put_user(info.pid, &infop->si_pid, Efault);
1640         unsafe_put_user(info.uid, &infop->si_uid, Efault);
1641         unsafe_put_user(info.status, &infop->si_status, Efault);
1642         user_write_access_end();
1643         return err;
1644 Efault:
1645         user_write_access_end();
1646         return -EFAULT;
1647 }
1648 
1649 long kernel_wait4(pid_t upid, int __user *stat_addr, int options,
1650                   struct rusage *ru)
1651 {
1652         struct wait_opts wo;
1653         struct pid *pid = NULL;
1654         enum pid_type type;
1655         long ret;
1656 
1657         if (options & ~(WNOHANG|WUNTRACED|WCONTINUED|
1658                         __WNOTHREAD|__WCLONE|__WALL))
1659                 return -EINVAL;
1660 
1661         /* -INT_MIN is not defined */
1662         if (upid == INT_MIN)
1663                 return -ESRCH;
1664 
1665         if (upid == -1)
1666                 type = PIDTYPE_MAX;
1667         else if (upid < 0) {
1668                 type = PIDTYPE_PGID;
1669                 pid = find_get_pid(-upid);
1670         } else if (upid == 0) {
1671                 type = PIDTYPE_PGID;
1672                 pid = get_task_pid(current, PIDTYPE_PGID);
1673         } else /* upid > 0 */ {
1674                 type = PIDTYPE_PID;
1675                 pid = find_get_pid(upid);
1676         }
1677 
1678         wo.wo_type      = type;
1679         wo.wo_pid       = pid;
1680         wo.wo_flags     = options | WEXITED;
1681         wo.wo_info      = NULL;
1682         wo.wo_stat      = 0;
1683         wo.wo_rusage    = ru;
1684         ret = do_wait(&wo);
1685         put_pid(pid);
1686         if (ret > 0 && stat_addr && put_user(wo.wo_stat, stat_addr))
1687                 ret = -EFAULT;
1688 
1689         return ret;
1690 }
1691 
1692 int kernel_wait(pid_t pid, int *stat)
1693 {
1694         struct wait_opts wo = {
1695                 .wo_type        = PIDTYPE_PID,
1696                 .wo_pid         = find_get_pid(pid),
1697                 .wo_flags       = WEXITED,
1698         };
1699         int ret;
1700 
1701         ret = do_wait(&wo);
1702         if (ret > 0 && wo.wo_stat)
1703                 *stat = wo.wo_stat;
1704         put_pid(wo.wo_pid);
1705         return ret;
1706 }
1707 
1708 SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
1709                 int, options, struct rusage __user *, ru)
1710 {
1711         struct rusage r;
1712         long err = kernel_wait4(upid, stat_addr, options, ru ? &r : NULL);
1713 
1714         if (err > 0) {
1715                 if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
1716                         return -EFAULT;
1717         }
1718         return err;
1719 }
1720 
1721 #ifdef __ARCH_WANT_SYS_WAITPID
1722 
1723 /*
1724  * sys_waitpid() remains for compatibility. waitpid() should be
1725  * implemented by calling sys_wait4() from libc.a.
1726  */
1727 SYSCALL_DEFINE3(waitpid, pid_t, pid, int __user *, stat_addr, int, options)
1728 {
1729         return kernel_wait4(pid, stat_addr, options, NULL);
1730 }
1731 
1732 #endif
1733 
1734 #ifdef CONFIG_COMPAT
1735 COMPAT_SYSCALL_DEFINE4(wait4,
1736         compat_pid_t, pid,
1737         compat_uint_t __user *, stat_addr,
1738         int, options,
1739         struct compat_rusage __user *, ru)
1740 {
1741         struct rusage r;
1742         long err = kernel_wait4(pid, stat_addr, options, ru ? &r : NULL);
1743         if (err > 0) {
1744                 if (ru && put_compat_rusage(&r, ru))
1745                         return -EFAULT;
1746         }
1747         return err;
1748 }
1749 
1750 COMPAT_SYSCALL_DEFINE5(waitid,
1751                 int, which, compat_pid_t, pid,
1752                 struct compat_siginfo __user *, infop, int, options,
1753                 struct compat_rusage __user *, uru)
1754 {
1755         struct rusage ru;
1756         struct waitid_info info = {.status = 0};
1757         long err = kernel_waitid(which, pid, &info, options, uru ? &ru : NULL);
1758         int signo = 0;
1759         if (err > 0) {
1760                 signo = SIGCHLD;
1761                 err = 0;
1762                 if (uru) {
1763                         /* kernel_waitid() overwrites everything in ru */
1764                         if (COMPAT_USE_64BIT_TIME)
1765                                 err = copy_to_user(uru, &ru, sizeof(ru));
1766                         else
1767                                 err = put_compat_rusage(&ru, uru);
1768                         if (err)
1769                                 return -EFAULT;
1770                 }
1771         }
1772 
1773         if (!infop)
1774                 return err;
1775 
1776         if (!user_write_access_begin(infop, sizeof(*infop)))
1777                 return -EFAULT;
1778 
1779         unsafe_put_user(signo, &infop->si_signo, Efault);
1780         unsafe_put_user(0, &infop->si_errno, Efault);
1781         unsafe_put_user(info.cause, &infop->si_code, Efault);
1782         unsafe_put_user(info.pid, &infop->si_pid, Efault);
1783         unsafe_put_user(info.uid, &infop->si_uid, Efault);
1784         unsafe_put_user(info.status, &infop->si_status, Efault);
1785         user_write_access_end();
1786         return err;
1787 Efault:
1788         user_write_access_end();
1789         return -EFAULT;
1790 }
1791 #endif
1792 
1793 /**
1794  * thread_group_exited - check that a thread group has exited
1795  * @pid: tgid of thread group to be checked.
1796  *
1797  * Test if the thread group represented by tgid has exited (all
1798  * threads are zombies, dead or completely gone).
1799  *
1800  * Return: true if the thread group has exited. false otherwise.
1801  */
1802 bool thread_group_exited(struct pid *pid)
1803 {
1804         struct task_struct *task;
1805         bool exited;
1806 
1807         rcu_read_lock();
1808         task = pid_task(pid, PIDTYPE_PID);
1809         exited = !task ||
1810                 (READ_ONCE(task->exit_state) && thread_group_empty(task));
1811         rcu_read_unlock();
1812 
1813         return exited;
1814 }
1815 EXPORT_SYMBOL(thread_group_exited);
1816 
1817 __weak void abort(void)
1818 {
1819         BUG();
1820 
1821         /* if that doesn't kill us, halt */
1822         panic("Oops failed to kill thread");
1823 }
1824 EXPORT_SYMBOL(abort);
1825 

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